A PHOTOEMISSION-STUDY OF THE INTERDIFFUSION OF SI IN ER FILMS DEPOSITED ON SI(111)(7X7) AT ROOM-TEMPERATURE

Er metal has been evaporated on clean Si(111)(7 X 7) substrates at room temperature and the Er-Si interaction at the interface studied by low energy electron diffraction (LEED), X-ray photoemission spectroscopy (XPS) and X-ray induced Auger electron spectroscopy (XAES). The use of the low and high energy X-ray lines given by the Zr anode (ZrM-xi and L-alpha) have allowed us to detect respectively the surface sensitive Si2p core-level and the chemical state sensitive SiKLL Auger transition, and hence, to evidence the inter-diffusion and to determine the nature of the reacted phase(s). A three-step mechanism has been found: formation of a chemisorbed layer until a critical coverage theta(c) almost-equal-to 0.8 ML (monolayer) is attained, inter-mixing reaction in the approximately 0.8-2.5 ML range giving a silicide-like layer, and growth of a nearly pure Er upper layer.